In the pregnant rabbit doe, follicular estrogens and the fetal placenta are required to maintain progesterone production by the corpora lutea (CL) during gestation. The fetal placenta exerts its effects on the CL through either an antiluteolytic and/or luteotropic mechanism. However, studies examining the gonadotropin-like activity of rabbit placentas have failed to identify any chorionic gonadotropin. Recent evidence suggests that the placenta may act as an indirect luteotropin by modifying pituitary or follicular secretions. We have identified a small peptide with both biological and immunological GnRH-like activity in the rabbit placenta. It is not clear whether the placenta synthesizes this molecule or merely binds GnRH found in the peripheral circulation. The specific aims of this proposal are: 1) to determine whether the rabbit fetal placenta synthesizes GnRH; 2) to determine whether GnRH is secreted by the rabbit placenta; 3) to localize the site of synthesis or binding of GnRH within the placenta; and 4) to quantitate changes in the levels of GnRH in the placenta throughout pregnancy. Synthesis of GnRH will be determined by incubating placentas with 3H-leucine and measuring the formation of 3H-GnRH in culture medium. Secretion of GnRH will be determined using a perifusion system and measuring the release of GnRH by placental tissue in response to pulses of 60mM K+. Localization of GnRH within the placenta will be achieved through immunofluorescence using a GnRH antibody linked to a fluorescent compound. Finally, placentas collected at days 12, 18, and 28 of gestation will be analyzed for GnRH content. These studies will extend our understanding of mechanisms involved in the maintenance of pregnancy. In addition, they will provide new information concerning extrahypothalamic sources of GnRH.